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<p>A <b>fraction diagram</b> shows the species distribution for a given chemical component.
Fraction values go from zero to one (0% to 100%) and are usually plotted against a
free concentration.
Example for the system <nobr>H<sup>+</sup>,</nobr>
<nobr>CO<sub>3</sub><sup>2&#8722;</sup>:</nobr></p>

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<center><img src="images/Diagr_Frac.gif" border="1" width="292" height="222" alt="Fraction diagram"></center>
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<p>This diagram was obtained with the following input file:</p>
<pre><code>2 4 0 0
H+, CO3-2
OH-,     -14.0 -1 0
CO2(g),   18.16 2 1
H2CO3(aq),16.68 2 1
HCO3-,    10.33 1 1
CO3-2,  H+,
LAV, -5.0 -11.0, T, 0.01</code></pre>

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